Bus duct plug-in device



March 24, 1964 N. B. PAPALAS BUS DUCT PLUG-IN DEVICE Filed Sept. 15, 1958 5 wwa mziyfim a i E 9L 5 z M M 2 J 4 Ti @J./ m w aa w H! 6/, a r ax a I flfifi M a xfl 3% m J w Q Q 1), a Z I 0 a L A Z 3 MM 1 G I F 0 z m ATTORNEY United States Patent" 3,126,241 BUS DUCT PLUG-IN DEVKCE Nicholas B. Papalas, Westfield, N.J., assignor to Federal Pacific Electric Company, a corporation of Delaware Filed Sept. 15, N58, Ser. No. 760,974 14 laims. (Cl. 339-22) This invention relates generally to a bus duct plug-in device. More particularly, the invention relates to a plugin device for a bus duct of the low reactance type in which the conductors are relatively closely spaced and operate at different potentials or are of different phases.

In the preferred embodiment of the invention to be described hereinafter, the bus duct has broad and thin bus bars arranged side by side with their broad faces opposed, in successive parallel planes. The contacts of the plug-in device are arranged to enter spaces between the bars to make contact with the broad faces of the bars in a manner consistent with the close spaced relationship. In the illustrated embodiment the bus bars are arranged in closely spaced pairs, with alternating narrow and wide spaces; and the plug-in device has one contact per pair of bars which projects intoa wide space between the close-spaced pairs of bars. Each contact engages only one surface of its respective bus bar. This is unlike the standard plug-in device contacts where ample spaces between bars accommodate the type of contact that grips a bar from opposite sides. Under abnormal or severe short circuit current conditions, 1 have found that contacts of the type that engage only one face of a bus bar are subject to arcing, burning, sticking, etc. Such damage, I have found, can be avoided through use of unusually heavy contact pressures.

The contacts of the illustrative plug-in device provide wiping action as they slide into engagement With the wide faces of the bus bars and even though each contact engages only one surface of its respective bus bar, each contact nevertheless applies contact pressure against its respective bus bar under normal conditions, without disturbing the important close spaced relationship between the bars. The contacts are arranged to provide for this firm contact pressure without requiring an inordinate amount of insertion effort.

An important feature of the present invention is the provision of a plug-in device having improved contacts of the aforenoted character which have requisite normal contact pressures and which provide for the contact pres sure between the contacts and their associated bus bar surfaces to be increased under abnormal or short-circuit conditions. As will be noted, the contacts are adapted to carry heavy currents and have yieldable contacts with the bus bars in the direction perpendicular to the length of the plug-in contacts.

Another object of the present invention is the provision in a plug-in device of the aforenoted character, of a generally improved contact assembly which is adapted to carry heavy currents reliably and efiiciently, and which may be economically mass produced and assembled.

Other objects, features and advantages of the present invention will become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings in which:

FIG. 1 is a front elevational view of a plug-in block or contact assembly formed according to the present invention;

FIG. 2 is a sectional view taken on the line 2-2 of FIG. 1;

FIG. 2A is a modification of a portion of FIG. 2;

FIG. 3 is a side elevational view showing a plug-in adapter, partially broken away to reveal a contact assembly, in operative assembly with a bus duct, the latter being shown in cross section; and

FIG. 4 is a side elevational view showing the contact assembly in operative engagement with a companion busbar under abnormal or short circuit conditions.

Referring to the drawing, there is shown in FIG. 3 a plug-in adapter or device 10 which is plugged into the bus duct 12, said device 10 having a bus duct plug-in unit 14 suitably connected thereto both electrically and mechanically. The unit .14 may be of any desired type, for example a switch for controlling an electric motor, it being understood that such switch controls the current supply to the motor or other current utilizing device and that the device 1G functions as a power take-off or connector from the bus duct to the current utilizing device through the unit or switch 14. if desired, the device 10 itself may contain controls such as switches, circuit breakers, etc.

The bus duct 12 of the illustrated embodiment is of the type disclosed in application Serial No. 626,133, filed December 4, 1956, in the name of Paul M. Christensen et al., for Plug-In Bus Duct, and assigned to the assignee herein, reference being made to said application for a detailed description of the bus-duct. In general, the bus duct 12 comprises a duct 16 enclosing an assembly of bus bars 18. The bus bars are aligned with each other with their edges in a pair of parallel planes and with their broad faces in successive parallel planes. Six bars are illustrated, with the bars arranged in three groups of two bars in each group. The bars of each group are close to each other and the groups are relatively widely spaced. In the illustrated embodiment the six bars are arranged for three-phase 3-wire transmission of power, bars 18A and 18A being interconnected to form one pole of the bus system. Similarly bars 18B and 18B and 18C and are interconnected at the ends of the unit length of bus duct. The bars are insulation covered except at their areas of contact with the connectors 24 to be de-' scribed, only one bar of each group having such area. This bus bar arrangement provides an effective lowinductance construction for transmitting three-phase power.

An insulating and bar-clamping structure 20 is provided for holding the bars in the desired spatial relationship. The structure 20 is covered by the wall 12A of the duct 16, except for an opening 21 therein. The opposite walls 12A and 12A of the duct are suitably secured to the opposite walls 12B and 12B in duct defining relation. The structure 20 is utilized for the additional function of receiving the plug-in devices .10 and for guiding the plugin devices into effective engagement with the bus bars as described in detail in the aforereferred to copending application.

A series of passages 22 are formed in structure 20 for the reception of the projecting stab contacts 24 of the plug-in device 10 so that the bus engaging portion 26 of each contact can bear against the bare contact areas of the bus bars previously mentioned.

Device 10 comprises an enclosure 28 of any suitable design and construction which houses a series of three companion plug-in block assemblies 30, as shown in FIGS. 1, 2 and 4, each block assembly having -a stab contact 24. The assemblies 3% are arranged in enclosure 28 to register their stab contacts 24 with the bus bars 18A, 18B and 18C of the duct 1:6, on the plug-in connection of device 10 to the bus duct.

Pursuant to the present invention, plug-in block assembly 3d comprises a molded insulating block 32 having a laterally yieldable stab contact 24 secured thereto by the bolt and nut, 34 and 36, respectively. The block is aper tured therethrough as indicated at 38 and contact 24 extends therethrough, the latter having a laterally projecting mounting part 40 which is seated on portion 42 of the block. The block further includes mounting flanges 41 and 43 formed integral therewith. Terminal defining fittings 44 have mounting flanges 46 which are secured to the block 32 by bolt 34. The part 40 is provided with a terminal 44 which is secured thereto by fastener 48. Thus the assembly includes three terminals 44, 44' which are connected to the contact 24. The contact 24 is of one-piece integral construction and includes a conductor part 24 and a bus engaging portion 26 which is bent back on part 24' in spaced relation therewith. Thus the contact 24 is characterized by a generally U-shaped terminal end having an inner straight leg portion defined by part 24 and an outer leg portion 26 defined by the adjacent arcuate portions 26 and 26", the latter defining a bus engaging or contacting area. Retained between said inner and outer leg portions by means of detents 50 is an insulating plate 52 which extends a short distance beyond outer leg 26. It will be noted that contact 24 is inclined slightly from a plane parallel to the plane of the opposite parallel side walls 54 and S6 of the block.

Extending through aperture 38 in laterally adjacent relation with contact 24 for coaction therewith is a backing member 58 which is preferably formed of steel. The member 58 has an upper laterally offset end part 60 and a connecting part 62 which are normally seated in recess 64 of the block. The part 60 is provided with a tongue 66 which extends into the slot 68 of contact part 40 for guiding the movement of member 58, said part 60 being laterally confined between the walls of recess 64. Seated between part 60 and the adjacent face of part 24' is a compression spring 70 which applies contact pressure to the contact 24 in the plugged-in condition of the unit. The block further includes a depending part or projection '72 having an abutment 74 for the member 58, said abutment defining a fulcrum for said member in the plugged-in condition of the unit. Projections 72 have inclined surfaces 76 which build up contact pressure during the insertion of the plug-in unit, and straight surfaces 76' (parallel to the wide faces of the bus bars) which maintain the contact pressure by reacting against the insulating structure 29. The opposite surfaces 78 of the projection 72 are also inclined, as best shown in FIG. 1, to the base wall 80 of the block, the latter Wall having laterally spaced depending ribs 82 which are adapted to seat against complementary formations of structure 20.

On the insertion of the plug-in units, contacts 24 engage the inclined surfaces 84 of the structure 29 and are guided across the contact areas at the broad face of the bus bars, the movement across the bus bars being a sliding action. This wiping or sliding contact is a highly desirable type of engagement. It will be noted that the surfaces 84 are aligned and merge with the contact faces of the bus bars. On this insertion of the plug-in units, the contacts 24 will be deflected towards their companion members 58 to engage the latter at 58', thereby pivoting the same about fulcrum 74 to concomitantly compress springs 70 which thereby apply contact pressure against the contacts in a bus bar engaging direction through said members. Accordingly, in the fully inserted position of the plug-in units, the portion 26" of each contact will be engaged with the bus bar contact areas and contact pressure will be. applied thereto by the spring biased member 58 which multiplies the bias of spring 70, fulcrum 74 being closer to bearing point 58' than to spring 70.

The structure includes insulating blocks 20' having cavities or pockets 22 for the reception of the stabs 24 of device 10, each block comprising end walls and a lateral wall 23 opposite the bus bars, and a base wall which defines a barrier to prevent accidental shortcircuiting of the bare areas of the bus bars to wall 12A of the duct enclosure when the plug-in devices are out of engagement with the bus duct. Thus the wall or barrier 25 prevents an instrument or device from crossing the bus bar with the Wall 12A of the enclosure, thereby enhancing the insulating effect of blocks 20'. The lateral wall 23 defines a'reaction surface to balance the forces applied between the stabs and bus bars on the insertion of the plug-in units, the surfaces 76, 76' coacting with said lateral wall as described in detail in the aforereferred to copending application.

The stab contacts 24 may be formed of any suitable conducting material, for example copper, soft or halfhard. It will be noted that the current paths of the stab contacts and bus bars are at right angles to each other. While the stab contacts are shown as comprising a conductor part 24 and bus engaging portion 26 of integral construction, it will be understood (see FIG. 2A) that said part and portion could, in concept, be of two parts 24a and 26a, hinge interconnected and provided with a conducting braid 2611.

Pursuant to the present invention, under abnormal or short circuit conditions, the contact pressure between the portions 26 and the bus bar contact areas will be increased to inhibit the separation thereof and the accompanying undesirable effects. Under such abnormal circuit conditions, a current surge results which produces a reaction in the form of a repelling force between the two parts 24' and 26 of the same conductor or contact. This reaction or repelling force (FIG. 4) produces a separation between the two parts 24' and 26 and since the bus bars are fixed in position further pivotal movement of the member 58 about its fulcrum 74 will take place and the spring 70 will be further compressed or loaded to thereby substantially increase the contact pressure of contact 24. Thus contact 24 will be spring biased into firmer engagement with the bus bar under fault current conditions due to the increase of compression of spring 70 which is brought about by the further pivotal movement of member 58, the tongue 66 riding in slot 68 on said pivotal movement. The member 58 provides a relatively long lever arm between the spring and the fulcrum 74 for transmitting the biasing force of the spring to the contact. From the above it will be apparent that the aforedescribed contact arrangement applies firm contact pressure under both normal and abnormal circuit conditions, without dis turbing the closed spaced relationship between the bus bars. The contacts are adapted to carry heavy currents and have yieldable contact with the bars in a direction perpendicular to the length of the contacts.

While there is shown and described herein certain specific structure embodying the invention it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concepts.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. A plug-in device for a bus duct of the type having a series of relatively thin and broad bus bars wherein the broad faces of the bus bars are disposed in successive parallel planes and the edges of the bus bars are disposed in a pair of planes substantially perpendicular to said successive parallel planes, said plug-in device having a series of conductive laterally yieldable contacts projecting from the device and extending in the direction of insertion into the duct, said contacts establishing lateral pressure engagement against only one broad face of each respective engaged bus bar, each of said contacts being bent back on itself to define laterally adjacent contact portions including a supporting portion. joined by a bend to a laterally adjacent terminal bus-engaging portion that extends from the bend in the direction opposite the direction of plug-in insertion, the latter being subjected to a separating force under abnormal current conditions to thereby increase said lateral pressure engagement and reaction means extending from the device and acting on said supporting portion to resist the displacement thereof during such abnormal current conditions.

2. A plug-in device for a bus duct of the type having a series of relatively thin and broad bus bars wherein the broad faces of the bus .bars are disposed .in successive parallel planes and the edges of the bus bars are disposed in a pair of planes substantially perpendicular to said successive parallel planes, said plug-in device having a series of projecting laterally yieldable contacts extending from the device in the direction of insertion into the duct, means for biasing said contacts in the direction perpendicular thereto in the inserted condition of the device for establishing lateral pressure engagement with a side face of the engaged bus bar, said means comprising spring biased levers fulcrumed intermediate the ends thereof and having one end in engaged relation with their respective contacts, each of said contacts having a bus engaging portion thereof bent back on itself to define laterally adjacent contact portions, the latter being subjected to a separating force under abnormal circuit conditions to thereby increase said lateral pressure engagement.

3. A plug-in device for a bus duct of the type having a series of relatively thin and broad bus bars wherein the broad faces of the bus bars are disposed in successive parallel planes and the edges of the bus bars are disposed in a pair of planes substantially perpendicular to said successive parallel planes, said plug-in device having a series of projecting laterally yieldable contacts extending from the device in the direction of insertion into the duct, means for biasing said contacts in the direction perpendicular thereto in the inserted condition of the device for establishing lateral pressure engagement with a side face of the engaged bus bar, each of said contacts having a generally U-shaped terminal end comprising spaced leg portions, whereby under abnormal circuit conditions the spacing between said leg portions is increased to thereby increase said biasing force and said lateral pressure engagement, said means comprising a lever spring biased at one end and having its opposite end in engaged relation with said contact in the region of said terminal end, said lever being fulcrumed intermediate the ends thereof and nearer said opposite end.

4. A plug-in device for a bus duct, comprising a support having a projecting laterally yieldable contact extending therefrom in the direction of insertion into the duct, said contact being spring biased in the direction perpendicular thereto in the inserted condition of the device for establishing lateral pressure engagement, said contact having a terminal bus engaging portion thereof bent back on and connected to a projecting portion of the contact to define closely spaced laterally adjacent contact portions, an element of insulation interposed between said portions of said contact, said portions being subjected to a separating force under abnormal circuit conditions to thereby increase said lateral pressure engagement.

5. A plug-in device for a bus duct, comprising a support having a projecting laterally yieldable contact extending therefrom in the direction of insertion into the duct, means for biasing said contact in the direction perpendicular thereto in the inserted condition of the device for establishing lateral pressure engagement, said contact having a generally U-shaped terminal end comprising spaced leg portions, said biasing means being operatively arranged with respect to said contact to provide for the increase of the biasing force on the increase of spacing between said leg portions under abnormal circuit conditions, said biasing means comprising a lever spring biased at one end and having its opposite end in engaged relation with said contact in the region of said terminal end, said lever being fulcrumed on said support intermediate the ends thereof and nearer said opposite end.

6. A plug-in device for a bus duct, comprising a support having a projecting laterally yieldable contact extending therefrom in the direction of insertion into the duct, means for biasing said contact in the direction perpendicular thereto in the inserted condition of the device for establishing lateral pressure engagement, said contact having a generally U-shaped terminal end comprising spaced leg portions, said biasing means being operatively arranged with respect to said contact to provide for the 6. increase of the biasing force on the increase of spacing between said leg portions under abnormal circuit conditions, said biasing means comprising a lever and a spring interposed between one end thereof and said contact, the opposite end of said lever being operatively engaged with said contact in the region of said terminal end, said lever being fulcrumed on said support intermediate the ends thereof and nearer said opposite end to provide a relatively long lever arm extending from said one end to said fulcrum.

7. A plug-in device for a bus duct, comprising a support having a projecting laterally yieldable contact extending therefrom in the direction of insertion into the duct, means for biasing said contact in the direction perpendicular thereto in the inserted condition of the device for establishing lateral pressure engagement, said contact having a generally U-shaped terminal end comprising spaced leg portions, said biasing means being operatively arranged with respect to said contact to provide for the increase of the biasing force on the increase of spacing between said leg portions under abnormal circuit condi tions, said biasing means comprising a lever spring biased at one end and having its opposite end in engaged relation with said contact in the region of said terminal end, said lever being fulcrumed on said support intermediate the ends thereof and nearer said opposite end, said spaced leg portions having an insulator plate secured therebetween, and the outer one of said leg portions comprising an arcuate part having a median bus engaging contact area.

8. In combination, a bus duct and a plug-in device therefor, said bus duct having a series of relatively thin and broad bus bars having their broad faces disposed in successive parallel planes, the edges of the bus bars being disposed in a pair of planes substantially perpendicular to said successive parallel planes, said plug-in device having a series of projecting laterally yieldable contacts extending from the device in the direction of insertion into the duct and said contacts being spring-biased in the direction perpendicular thereto in the inserted condition of the device for establishing lateral pressure engagement against only one broad face of each respective engaged bus bar, each of said contacts having a bus engaging portion thereof bent back on itself to define a generally U.- shaped contact terminal end having a pair of closely spaced leg portions, an element of insulation interposed between said leg portions of said contact, whereby under abnormal circuit conditions the spacing between said leg portions is increased to thereby increase said lateral pressure engagement.

9. In combination, a bus duct and a plug-in device therefor, said bus duct having a series of relatively thin and broad bus bars having their broad faces disposed in successive parallel planes, the edges of the bus bars being disposed in a pair of planes substantially perpendicular to said successive parallel planes, said plug-in device hav ing aseries of projecting laterally yieldable contacts extending from the device in the direction of insertion into the duct and said contacts being spring-biased in the direction perpendicular thereto in the inserted condition of the device for establishing lateral pressure engagement against only one broad face of each respective engaged bus bar, each of said contacts having a bus engaging por* tion thereof bent back on itself to define a generally U- shaped contact terminal end having a pair of spaced leg portions, whereby under abnormal circuit conditions the spacing between said leg portions is increased to thereby increase said lateral pressure engagement, and means for spring biasing each of said contacts, said biasing means comprising a lever spring biased at one end and having its opposite end in engaged relation with said contact in the region of said terminal end, said lever being fulcrumed intermediate the ends thereof and nearer said oppoiste end.

10. In combination, a bus duct and a plug-in device therefor, said bus duct having a series of relatively thin and broad bus bars having their broad faces disposed in successive parallel planes, the edges of the bus bars being disposed in a pair of planes substantially perpendicular to said successive parallel planes, said plug-in device having a series of projecting laterally yieldable contacts extending from the device in the direction of insertion into the duct and said contacts being spring-biased in the direction perpendicular thereto in the inserted condition of the device for establishing lateral pressure engagement against only one broad face of each respective engaged bus bar, each of said contacts having a bus engaging portion thereof bent back on itselfto define a generally U-shaped contact terminal end having a pair of spaced leg portions, whereby under abnormal circuit conditions the spacing between said leg portions is increased to thereby increase said lateral pressure engagement, each of said contacts projecting from a companion support, and means for spring biasing each of said contacts, said biasing means comprising a lever and a spring interposed between one end thereof and said contact, the opposite end of said lever being operatively engaged with said contact in the region of said terminal end, said lever being fulcrumed on said support intermediate the ends thereof and nearer said opposite end to provide a relatively long lever arm extending from said one end to said fulcrum.

11. A plug-in device for a bus duct including an enclosure with plural bars therein, said plug-in device having insulating supporting means and a series of conductive laterally yieldable contacts extending from the device in the direction of insertion into the duct and projecting into a position of clearance in relation to said supporting means, and said contacts having spring biasing means effective to provide lateral pressure contact engagement with respective bus bars, the projecting end of each said contact being in the form of a reverse bend including a terminal bus engaging portion and a series-connected laterally adjacent portion closely spaced from said bus engaging portion, said reverse bend being subjected to an expanding force under abnormal circuit conditions to thereby increase said lateral pressure engagement, and an element of insulation separating said bus engaging portion from said lateraly adjacent portion of each said projecting contact. I

12. A plug-in device for bus duct having a series of bus bars in an enclosure provided with a plug-in opening, said plug-in device having a series of conductive laterally yieldable contacts projecting from the device and extending in the direction of insertion into the duct and said contacts having spring-bias means acting to bias the contacts in the direction perpendicular to said extending direction for establishing lateral contact pressure against respective bus bars, each of said contacts including a bus engaging leg disposed laterally of and closely adjacent to a companion leg, said legs extending, respectively, along and opposite said direction of insertion and said legs being connected together to provide a reverse-bend current path whereby under abnormal circuit conditions the spacing between the legsis increased to thereby increase said lateral pressure engagement, and an element of insulation interposed between said legs.

13. A plug-in device for a bus duct as recited in claim 12, said plug-in device further including mechanical reaction means acting on a projecting portion of said companion leg to resist displacement thereof during the aforesaid abnormal circuit conditions.

14. The combination as set forth in claim 13, wherein said plug-in device includes mechanical reaction means acting on that leg portion which is opposite said bus engaging portion to resist the displacement thereof under abnormally high current conditions.

References Cited in the file of this patent UNITED STATES PATENTS 746,580 Russell Dec. 8, 1903 1,253,874 Paiste Jan. 15, 1918 2,037,026 Hubbell Apr. 14, 1936 2,262,067 Togesen et a1 Nov. 11, 1941 2,309,611 Harvey Jan. 26, 1943 2,318,860 Huguelet May 11, 1943 2,328,318 Wood Aug. 31, 1943 2,452,019 Rowe Oct, 19, 1948 2,482,310 Adam Sept. 20, 1949 2,526,201 Daly Oct. 17, 1950 2,695,350 Schultz Nov. 23, 1954 2,720,632 Stieglitz Oct. 11, 1955 2,759,076 Curtis Aug. 14, 1956 2,968,781 Staskowiski Jan. 17, 1961 

2. A PLUG-IN DEVICE FOR A BUS DUCT OF THE TYPE HAVING A SERIES OF RELATIVELY THIN AND BROAD BUS BARS WHEREIN THE BROAD FACES OF THE BUS BARS ARE DISPOSED IN SUCCESSIVE PARALLEL PLANES AND THE EDGES OF THE BUS BARS ARE DISPOSED IN A PAIR OF PLANES SUBSTANTIALLY PERPENDICULAR TO SAID SUCCESSIVE PARALLEL PLANES, SAID PLUG-IN DEVICE HAVING A SERIES OF PROJECTING LATERALLY YIELDABLE CONTACTS EXTENDING FROM THE DEVICE IN THE DIRECTION OF INSERTION INTO THE DUCT, MEANS FOR BIASING SAID CONTACTS IN THE DIRECTION PERPENDICULAR THERETO IN THE INSERTED CONDITION OF THE DEVICE FOR ESTABLISHING LATERAL PRESSURE ENGAGEMENT WITH A SIDE FACE OF THE ENGAGED BUS BAR, SAID MEANS COMPRISING SPRING BIASED LEVERS FULCRUMED INTERMEDIATE THE ENDS THEREOF AND HAVING ONE END IN ENGAGED RELATION WITH THEIR RESPECTIVE CONTACTS, EACH OF SAID CONTACTS HAVING A BUS ENGAGING PORTION THEREOF BENT BACK ON ITSELF TO DEFINE LATERALLY ADJACENT CONTACT PORTIONS, THE LATTER BEING SUBJECTED TO A SEPARATING FORCE UNDER ABNORMAL CIRCUIT CONDITIONS TO THEREBY INCREASE SAID LATERAL PRESSURE ENGAGEMENT. 